The invention relates generally to the area of machine controllers; and specifically, the invention provides apparatus for interfacing machine contact information between a programmable machine function controller and another numerical control.
Ever since the advent of numerical controls, the interface of the numerical control to a machine has been the source of high labor and material costs and reliability problems in the numerical control. In addition to providing slide control information, i.e. electrical signals to control the displacement and velocity of the machine slides, the numerical control must communicate with the machine to control many of its other functions, e.g. tool selection, spindle direction and speed, coolant selection axis permission and overtravel, etc. These signals may vary from DC control levels to standard AC voltage levels. Therefore, a typical numerical control may require hundreds of interconnecting wires between it and the machine. This wiring is expensive from a material and labor standpoint the first time the machine is assembled in the manufacturer's facility. Each time the machine is moved for shipping or other purposes, the costs are intensified because the wiring must be disconnected and later reconnected. Second, the presence of the various machine control signals, many having inductive loads, in the same control cabinet as the digital logic circuits, inevitably will lead to noise and reliability problems in the numerical
To avoid these problems, numerical control manufacturers may use one or more levels of interfacing circuits. A typical example of this may include for each machine control signal the serial combination of an optical isolator, an output drive transistor, a miniture relay, a level shifting amplifier and a high voltage digital switching stage. The inclusion of such circuits for each of the machine control signals is obviously very expensive.
The use of direct wiring of machine to numerical controls did not change until the introduction of programmable machine function controllers which have been commerically available for at least the last five years. The controllers are used to replace the machine magnetic relay circuits and execute the logical operations previously executed by said relay circuits. Consequently, the numerical control is wired directly to the controller and the machine. The use of programmable controllers alleviates some of the problems.
A solution to the extensive wiring required is disclosed by the apparatus discussed in U.S. Pat. No. 3,810,104. According to this patent, the ideal programmable controller should be capable of handling all types of machines. This requires a storage area within the controller sufficient to store all existing machine control signals. However, any one machine may only require one-third to one-half of the total number of signals. Therefore, the patent discloses an apparatus having a memory with a limited storage capacity and an interface circuit for receiving the machine control signals and decoding these signals into addresses usable by the limited storage. Further, the wiring problem is simplified by multiplexing the signals between the numerical control and the controller. The system disclosed in the patent requires control circuits for synchronizing the operation of the interface circuit with the programmable controller. In the prior art system, the programmable controller generates an address signal to the interface circuit and waits for a word corresponding to that address to be returned. This synchronous operation increases the complexity of the timing control circuits required by the programmable controller. Further, the system only provides for the communication of the machine control signals from a numerical control to the programmable controller.
In contrast, the single bit contact interface circuit disclosed herein operates asynchronously with the machine controller and the numerical control, thereby reducing the complexity of the timing control circuits within the programmable controller and the numerical control and improving the reliability of the overall system. Further, the interface circuit disclosed herein is bidirectional; and it is direct in that an intermediate interface decoding stage is not required. All of the contact information is cyclically and continuously transferred between both ends of the interface circuit for use by the numerical control and the machine controller. Further, the transfer of the information does not effect the normal operation of the numerical control or the machine controller. The interface circuit is, in effect, transparent, and the numerical control and machine controller operate completely independently but each using contact information generated by the other. Not only does the interface circuit reduce the amount of wiring required to pass machine control signals between the machine controller and the numerical control, but it provides a hardware standardization for transferring contact information between the machine controller and many types of numerical controls.